The present invention relates to brush actuator mechanisms for rotating electrical machines; and more particularly, the invention relates to a brush actuator mechanism for a homopolar generator.
Pulsed homopolar generators (HPGs) are rotating, electrical machines which are being developed as pulsed power supplies for applications that include electromagnetic propulsion, welding, and fusion devices. These machines are inherently low voltage, very high current generators. In designing a pulsed HPG for many applications one tries to obtain a maximum machine voltage for a given rotor size (rotor size determines energy level) resulting in a minimum effective capacitance. A minimum capacitance results in a maximum transfer efficiency of the HPG energy into the load. HPG voltage is proportional to the rotational speed of the rotor .omega. and the total amount of flux cut by the rotor .phi.: EQU V=.omega..phi./2.pi.
As the rotational speed is limited by physical properties of the rotor and current collection system and the flux density in a ferromagnetic material is limited to about 2.0 Tesla because of magnetic saturation effects, the most effective way to increase machine voltage is to increase the flux-cutting area of the rotors. In a homopolar generator configured with an inner brush mechanism housed within a stator support structure by disposition of the field coil and inner brush mechanism within a recess in the periphery of the rotor, an increase in the flux-cutting area of the rotor can be accomplished by minimizing the radial height of the field coil and inner brush mechanism.
Decreasing the radial height of the field coil is limited by the required ampereturn rating. Therefore the most expedient way to increase voltage is to decrease the radial height of the inner brush mechanism. However, it is necessary to be able to retract or lower the brushes on demand in order to minimize brush wear and losses. Most ferromagnetic HPG designs of either disk or drum configurations suffer from similar limitations. In earlier machines, the brushes were actuated by air cylinders. However, the radial height penalty for using an air cylinder is unacceptable on the compact HPG configurations and is a serious compromise on any HPG design.